The present invention relates to disc drives. More particularly, the present invention relates to writing data to a reassigned sector from a defective sector.
A typical disc drive includes one or more transducers supported by an air bearing relative to each disc. The transducers and the air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the discs and to store information on the discs.
An actuator typically operates within a closed-loop servo system. The actuator typically includes an actuator arm that supports a flexure or flexure assembly which, in turn, supports the data head. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations. The time when the data head is near a target track and fine tuning its position just prior to commencing track following is referred to as track settle or seek settle.
Information is typically stored on the discs by providing a write signal to the data head to encode information on the surface of the disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the servo actuator so that the data moves over the disc, sensing the data on the disc, and generating a read signal based on that information. The read signal is then decoded by the drive controller to recover the data represented by the information stored on the disc, and consequently represented in the read signal provided by the data head.
Data can be written to the disc in sectors. However, it sometimes happens that sectors are defective. The disc is typically verified during the manufacturing process. If the defective sectors are found during a factory defect scan, they are added to a defective sector list and they are simply skipped during assignment of logical block addresses. This is sometimes referred to as slipping the sector. In that case, as the disc drive is writing data to the disc, it simply skips those sectors when data is written.
However, it also sometimes happens that sectors become defective during normal operation of the disc, and after the factory defect scan has been performed. In that case, the sectors can not be slipped because the subsequent sectors may already have data written on them. In order to accommodate such defective sectors, the drive controller reserves a spare pool of reassignment sectors. The spare pool of reassignment sectors typically contains a number of unused sectors, near the end of the disc, which are used to replace the defective sectors.
By way of example, if the disc drive is to write ten sectors (sectors 0-9) and two sectors (sectors 3 and 6) are found to be newly defective during operation of the drive, the drive controller will reassign the logical block address of the newly defective sectors to the spare pool of reassignment sectors. Subsequent write operations in these sectors (sectors 0-9), where reassignment has been performed, requires the following sequence:
First, sectors 0-2 are written, and the write operation is stopped.
Next, the drive controller seeks to the spare pool of reassignment sectors, and sector 3 is written to the spare pool.
The drive then seeks back to the original track and writes sectors 4-5.
The write operation is again stopped, and the drive seeks to the spare pool of reassignment sectors where sector 6 is written.
Finally, the drive seeks back to the original track again where sectors 7-9 are written.
It can be seen that writing the reassigned sectors requires multiple seeks during the original write operation. This slows down the access time required to write all of the data sectors.
A method of writing to a disc in a disc drive includes receiving data to be written to a designated area of the disc wherein the designated area has a beginning, an end, and contains a defective portion. The data is written to the disc starting from the beginning of the designated area and proceeding toward the end of the designated area. The data is written to a temporary buffer, external to the disc, upon reaching the defective portion of the designated area. Writing is then resumed, writing data to the designated area of the disc, upon passing the defective portion of the designated area.
In one illustrative embodiment, the disc includes a reassignment portion located discontiguously from the designated area where the data is to be written. The write operation to the designated portion of the disc is completed and then the drive seeks to a reassignment portion of the disc. Data is then written from the temporary buffer to the reassignment portion of the disc.
In yet another illustrative embodiment, prior to writing data to the temporary buffer, it is determined whether the temporary buffer is full. If so, the drive seeks to the reassignment portion of the disc and writes the data from the temporary buffer to the reassignment portion, prior to completing the write operation in the designated area. In still another illustrative embodiment, the drive does not seek to the reassignment portion of the disc until the temporary buffer is full.